(1) Field of the Invention
The present invention relates to processes used to fabricate semiconductor devices, and more specifically to a method of forming a capping layer on a copper structure, wherein the capping layer improves the adhesion between the copper structure and overlying materials.
(2) Description of Prior Art
Micro-miniaturization, or the ability to fabricate semiconductor devices with sub-micron features, has allowed the performance of the sub-micron devices to be increased. The use of smaller device features have resulted in a reduction of performance degrading parasitic junction capacitances enabling the desired device performance increase to be realized. In addition the use of low dielectric constant materials, as well as the use of more conductive interconnect materials such as copper, have also contributed to device performance enhancements. However the use of the above materials such as copper for interconnect structures, has brought attention to specific process and structural concerns which were not as crucial with other interconnect structures, structures fabricated with materials such as aluminum. For example the adhesion between a copper damascene structure and overlying layers or structures, such as a silicon nitride etch stop layer, or an overlying upper level conductive interconnect structure, can be marginal possibly resulting in yield loss or reliability degradation. The thickness of materials overlying the copper damascene structure have to be carefully chosen as well as carefully prepared or formed, to reduce the risk of adhesion loss to the underlying copper structure.
This invention will describe a novel process sequence for improving the adhesion between a copper structure and overlying materials via the use of a capping layer formed on the copper structure, wherein the capping layer is obtained using a specific mode of deposition as well as using specific deposition conditions. Prior art, such as Shih et al, in U.S. Pat. No. 6,391,780 B1, Roy in U.S. Pat. No. 6,004,188, and Ohashi et al in U.S. Pat. No. 6,403,459 B1, describe methods of forming copper structures, methods of forming damascene structures, and methods of improving adhesion between copper structures and adjacent materials. These prior art however do not describe the novelty of this present invention in which a specific capping layer material, deposited via a specific deposition mode using specific deposition conditions, is employed to improve the adhesion between a copper damascene structure and overlying layers and structures.